In holes What was the source of the foul Odor Stanley smelled on the mountain?

In "Holes" by Louis Sachar, the foul odor that Stanley smells on the mountain comes from the remains of a long-dead animal, specifically a skunk. This smell is associated with the area around the hole where he and the other boys dig, as they often encounter various unpleasant scents while working at Camp Green Lake. The odor serves to emphasize the harsh and unappealing environment of the camp.